This invention relates generally to belt, or chain, conveyors for transporting articles on an article-conveying surface and, more particularly, to changing the surface characteristics of the article-conveying surface of such a belt or chain.
Plastic conveyor belts, or chains, are used widely in the food-processing industries to convey food products. In the beverage industry, for instance, belts are used to convey bottles. In certain applications, bottles must be conveyed up an inclined path. Because of the inherent slickness of most plastic belt materials, the slope of the incline must be limited lest the bottles slip on the slick conveying surface of the belt. For some plastic belt materials, such as acetal, the maximum slope may be limited to only a few degrees off horizontal. Flights or buckets are used in some applications to convey products uphill, but they form barriers on the conveying surface that are unacceptable in other applications. High-friction rubber-like materials inserted into or directly molded onto the slick plastic conveying surface are especially effective in transporting packages up steep inclines, but would impede the rapid transfer of bottles between belts required in many beverage applications. Thus, there is a need for a belt conveyor that provides just enough friction on its article-conveying surface to convey articles up shallow inclines without slippage and yet not so much friction that the rapid transfer of articles to and from the conveying surface is impeded.
In other applications, other belt surface properties are desirable. Properties such as low-friction, electrical conductivity, and non-stick, are typically achieved by manually applying materials having the desired property directly on the belt surface or by compounding appropriate materials into a plastic resin before molding a belt module. The manual application and re-application of these materials as they are used up can be messy and time-consuming. While molding belt modules out of certain materials may give the desired benefits, there can be unwanted side-effects, such as brittle or weak belt structure, caused by the incorporation of the materials having the desired characteristics. Thus, there is a further need for transferring a variety of surface characteristics to a belt surface.
These needs and others are satisfied by a belt conveyor having features of the invention. The preferred conveyor includes a plastic conveyor belt, driven by a belt drive, and a transfer element disposed close to a surface of the belt. The transfer element transfers coating material to the surface of the belt along a section of the belt-conveying path. The transferred material has properties that change the effective surface characteristics of the belt. As the belt is driven past the transfer element, the coating material is transferred onto the belt surface, thereby changing its effective properties.
In one version of the conveyor, the transfer element is an applicator that includes a reservoir for the coating material. The reservoir is preferably easy to replenish.
Another version of a conveyor includes, as a transfer element, a bearing element with a bearing surface made of an oxidizable metal. The bearing element bears against the slick article-conveying surface of the belt along a section of the belt-conveying path. As the belt is driven past the bearing element, the oxidizable metal on the bearing surface is transferred onto the article-conveying surface of the belt. The transferred metal, which soon oxidizes, forms an oxide layer atop the article-conveying surface. The oxide layer exhibits increased friction compared with the slick plastic of the belt. In this way, the invention provides a belt and a conveyor system with just enough friction to transport bottles up modest inclines without also impeding the rapid transfer of bottles across the article-conveying surface. Thus, the objective of providing a belt with generally desirable low-friction characteristics with a slight amount of friction only on the articleconveying surface to prevent conveyed articles from slipping is achieved.
In a preferred version of the invention, the metal constituting the bearing surface is selected from the group consisting of aluminum, stainless steel, and carbon steel. Of these, aluminum is most preferred because of its relative softness, ready oxidation in typical environments, inexpensive cost, and ready availability. In other versions of the invention, the bearing element can be stationary, weighted down against the articleconveying surface by weights, and disposed at a position on the belt-conveying path where articles are not on the belt.
In yet another version of the invention, surface properties are transferred to the article-conveying surface of the belt by the conveyed articles themselves after contact with a source of the preselected material.
In a method according to the invention, the friction of a belt""s conveying surface is increased by positioning a bearing element with a bearing surface made of an oxidizable metal in contact with the conveying surface of a conveyor belt. The conveyor belt and the bearing element in contact are moved relative to each other. The relative motion transfers the oxidizable metal from the bearing surface to the article-conveying surface, thereby increasing the friction with conveyed articles.
In another version, a method is provided for forming a thin layer of a preselected coating material on a surface of a conveyor belt. Because the transfer element is positioned close to the belt surface, the coating material fed from the transfer element is transferred by rubbing as a thin layer on the belt surface. Materials are selected to provide surface characteristics different from those of an unlayered surface. The material can even be replenished as it is spent. Thus, surface characteristics other than increased friction can be simply imparted to a conveyor belt to handle a variety of applications.